The present invention relates to a gate oxide, and more particularly to a method for improving the electrical properties of a gate oxide.
As a result of the mushroom growth of microcircuit technology, the dimension of the semiconductor element is getting small. Nowadays, in order to develop the sub-micron technology applied in the field of ULSI (ultra-large-scale integration) circuit, the thickness of gate oxide is dropped below 100 xc3x85 A as well. In a wide variety of the approaches for growing the gate oxide, the thermal oxidation process is widely used. The trend of developing the thermal oxidation process is focused on how to manufacture a thin and high-quality gate oxide in concord with the requirement of the gate oxide in a ULSI circuit. Thus, the gate oxide must own the characteristics of high dielectric constant, low oxide charge, high breakdown voltage, and so forth.
The conventional approach for growing an oxide layer is carried out in a heating tube. However, the conventional approach for growing a gate oxide is gradually replaced by rapid thermal oxidation (RTO). Currently, the two-step rapid thermal oxidation (RTO) followed by rapid thermal annealing (RTA) has been used for making thin and high-quality oxides. Generally, there are two approaches applied in the growth of the gate oxide: (1) performing thermal oxidation in the presence of a pure and dry oxygen, followed by rapid thermal annealing in the presence of nitrogen, and (2) performing thermal oxidation under the atmosphere of nitrous oxide, followed by rapid thermal annealing in the presence of nitrogen. Though the gate oxide grown by the above approach has a dense structure and can suffer a high breakdown electric field and can score higher charge-to-breakdown, its thickness is not uniform. It will cause the unstable gate oxide in the subsequent fabrication process.
Therefore, an object of the present invention is to provide a method for improving the breakdown electric field strength and increasing the charge-to-breakdown of the gate oxide.
Another object of the present invention is to form the gate oxide with uniform thickness.
According to the present invention, the gate oxide is formed by the following steps: (a) providing a silicon wafer with a gate oxide formed thereon, (b) providing a specific metal plate, (c) immersing the silicon wafer and the specific metal plate in a chemical solution, (d) respectively connecting the silicon wafer and the specific metal plate with a current source and inducing an electron current to flow from the current source through the gate oxide of the silicon wafer to the specific metal plate, (e) removing the silicon wafer from the chemical solution and removing the residual chemical solution from the surface of the gate oxide, and (f) treating the gate oxide with an annealing process.
Certainly, before the gate oxide is grown on the surface of the silicon wafer, it is necessary to clean the surface of the silicon wafer by the RCA (Radio Corporation of America) clean process.
Preferably, the gate oxide is formed by a thermal oxidation process, such as a rapid thermal oxidation (RTO) process. Preferably, the gate oxide can be made of silicon oxide (SiO2), silicon nitride (Si3N4), or tantalum oxide (Ta2O5).
Preferably, the specific metal plate is a platinum plate. The platinum plate is electrically connected to the positive terminal of the current source to serve as an anode, and the silicon wafer is electrically connected to the negative terminal of said current source to serve as a cathode.
Certainly, the chemical solution has a relatively high electrical conductivity.
Preferably, the chemical solution is a diluted hydrofluoric acid (HF) solution having a concentration ranged from 0.049% to 0.98%, and more preferably 0.245%.
Preferably, the electron current has a current density ranged from 0.1xcexcA/cm2 to 10 xcexcA/cm2, and more preferably 4 xcexcA/cm2.
Certainly, the step of removing the residual chemical solution from the surface of the gate oxide is carried out by cleaning the surface of said gate oxide by the deionized water.
Certainly, the annealing process is a rapid thermal annealing (RTA) process.
Now the foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the accompanying drawings, in which: